Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. In addition, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV) and hybrid electric vehicles (HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuels.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, middle or large-sized devices, such as vehicles, use a middle or large-sized battery pack having a plurality of battery cells electrically connected to each other because high output and large capacity are necessary for the middle or large-sized devices.
Preferably, the middle or large-sized battery pack is manufactured so as to have as small a size and weight as possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell of the middle or large-sized battery pack. In particular, much interest is currently focused on such a pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the pouch-shaped battery is lightweight and the manufacturing cost of the pouch-shaped battery is low.
FIG. 1 is a perspective view typically showing a conventional representative pouch-shaped battery. Referring to FIG. 1, the pouch-shaped battery 100 is configured to have a structure in which two electrode leads 110 and 120 protrude from the upper end and the lower end of a battery body 130, respectively, such that the electrode leads 110 and 120 are opposite to each other. A sheathing member 140 includes upper and lower sheathing parts. That is, the sheathing member 140 is a two-unit member. In a state in which an electrode assembly (not shown) is mounted in a receiving part which is defined between the upper and lower sheathing parts of the sheathing member 140, opposite sides 142 and upper and lower ends 141 and 143, which are contact regions of the upper and lower sheathing parts of the sheathing member 140, are bonded to each other, whereby the pouch-shaped battery 100 is manufactured.
The sheathing member 140 is configured to have a laminate structure of a resin layer/a metal film layer/a resin layer. Consequently, it is possible to bond the opposite sides 142 and the upper and lower ends 141 and 143 of the upper and lower sheathing parts of the sheathing member 140, which are in contact with each other, to each other by applying heat and pressure to the opposite sides 142 and the upper and lower ends 141 and 143 of the upper and lower sheathing parts of the sheathing member 140 so as to weld the resin layers thereof to each other. According to circumstances, the opposite sides 142 and the upper and lower ends 141 and 143 of the upper and lower sheathing parts of the sheathing member 140 may be bonded to each other using a bonding agent. For the opposite sides 142 of the sheathing member 140, the same resin layers of the upper and lower sheathing parts of the sheathing member 140 are in direct contact with each other, whereby uniform sealing at the opposite sides 142 of the sheathing member 140 is achieved by welding. For the upper and lower ends 141 and 143 of the sheathing member 140, on the other hand, the electrode leads 110 and 120 protrude from the upper and lower ends 141 and 143 of the sheathing member 140, respectively. For this reason, the upper and lower ends 141 and 143 of the upper and lower sheathing parts of the sheathing member 140 are thermally welded to each other, in a state in which a film type sealing member 160 is interposed between the electrode leads 110 and 120 and the sheathing member 140, in consideration of the thickness of the electrode leads 110 and 120 and the difference in material between the electrode leads 110 and 120 and the sheathing member 140, so as to improve sealability of the sheathing member 140.
However, the mechanical strength of the sheathing member 140 is low. For this reason, battery cells (unit cells) are mounted in a pack case, such as a cartridge, to manufacture a battery module having a stable structure. However, a device or a vehicle, in which a middle or large-sized battery module is installed, has a limited installation space. Consequently, in a case in which the size of the battery module is increased due to the use of the pack case, such as the cartridge, the spatial utilization is lowered. In addition, the battery cells repeatedly expand and contract during charge and discharge of the battery cells due to the low mechanical strength of the battery cells. As a result, the thermally welded regions of the sheathing member may be easily separated from each other.
In addition, a battery pack is a structural body constituted by combining a plurality of battery cells and, therefore, safety and operational efficiency of the battery pack are greatly lowered when some of the battery cells suffer from overvoltage, overcurrent, or overheating. For this reason, means to sense such overvoltage, overcurrent, or overheating are needed. Consequently, voltage sensors, temperature sensors, etc. are connected to the respective battery cells to check and control operational states of the battery cells in real time or at predetermined intervals. Installation or connection of such sensing means very complicates a process of assembling the battery pack. Furthermore, a plurality of wires is needed to install or connect the sensing means with the result that a short circuit may occur in the battery pack.
In addition, in a case in which a middle or large-sized battery module is configured using a plurality of battery cells or a middle or large-sized battery pack is configured using a plurality of unit modules each including a predetermined number of battery cells, a plurality of members for mechanical fastening and electrical connection between the battery cells or the unit modules is generally needed and, as a result, a process for assembling the mechanical fastening and electrical connection members is very complicated. Furthermore, there is needed a space for coupling, welding, or soldering the mechanical fastening and electrical connection members with the result that the total size of the system is increased. The increase in size of the system is not preferable in the aspect of the spatial limit of an apparatus or device in which the middle or large-sized battery module is installed. Moreover, the middle or large-sized battery module must be configured to have a more compact structure such that the middle or large-sized battery module can be effectively installed in a limited inner space, such as a vehicle.
In connection with this respect, Japanese Patent Application Publication No. 2005-050616 discloses a middle or large-sized battery module installed in a large-sized vehicle, such as a bus, configured to have a structure in which the battery module includes a lower rack in which two battery packs are disposed and an upper rack in which two battery packs are disposed, a stand member of the lower rack and a stand member of the upper rack are suspended from a body of the vehicle via a suspension member of the lower rack and a suspension member of the upper rack, the stand members exhibit high strength, and the suspension members exhibit low strength, thereby improving safety of the battery module against external force applied to the battery module due to a vehicle crash.
In the above-described middle or large-sized battery module, a plurality of racks is used to improve safety of the vehicle when a vehicle crash occurs. However, two complicated racks are provided to install a total of four battery packs with the result that volume and weight of the battery module are increased. Consequently, it is technically difficult to configure the battery module such that the battery module has a compact structure. That is, the above technology has problems in that the external form of the battery module must be greatly increased to provide high mechanical strength, whereby the volume and weight of the battery module are greatly increased.
Meanwhile, a battery module assembly is a structural body constituted by combining a plurality of battery cells and, therefore, safety and operational efficiency of the battery module assembly are greatly lowered when some of the battery cells suffer from overvoltage, overcurrent, or overheating. For this reason, means to sense and control such overvoltage, overcurrent, or overheating are needed. Consequently, voltage sensors, temperature sensors, etc. are connected to the respective battery cells to check and control operational states of the battery cells in real time or at predetermined intervals. Installation or connection of such sensing means and control means very complicates a process of assembling the battery module. Furthermore, a plurality of wires is needed to install or connect the sensing means and the control means with the result that a short circuit may occur in the battery module.
Therefore, there is a high necessity for a battery module assembly, the structure of which is more compact, structural stability of which is high, and to which sensing means can be mounted through a simple structure as described above.